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Bringing the Solar Fire to Earth: Fusion Research

On the way towards an international fusion reactor

In the south of France, the international fusion reactor known as ITER is currently being constructed. For fusion researchers worldwide, this is the most important large-scale experiment, as ITER will be the first reactor to generate 500 million watts of fusion power in pulsed operation for around eight minutes. ITER will help to answer open questions before the first demonstration power plant for fusion power (DEMO) goes into operation. Whether this will be successful and whether we will come closer to the dream of an almost inexhaustible and clean source of energy essentially depends on the resistance of the reactor’s inner walls against heat and plasma particles. Jülich scientists have special expertise in the development of suitable wall concepts with resistant wall materials.

Fusion has enormous potential. The energy required by a family of four in Germany over a period of one year could be covered by around 2 litres of water and 250 grams of stone. This is based on the assumption that we will succeed in imitating the processes that occur inside the sun in power plants. In other words, we must first be able to use the fusion of light atomic nuclei to generate energy. This is the aim of fusion research. The advantages are that the light atomic nuclei lithium and deuterium can be readily extracted from natural resources, fusion processes are inherently safe and the formation of long-lived radioactive waste can be minimized by selecting suitable materials for the construction of the reactor.

Controlling plasma with a temperature of 100 million degrees

The challenge involves reconstructing conditions as they exist inside the sun in a fusion device – or to put it another way, keeping plasma with a temperature of 100 million degrees stable despite all of the processes that occur between the plasma and the surrounding vacuum vessel walls. Jülich scientists are experts in investigating this process, which is known as plasma-wall interaction and represents one of the keys for constructing future fusion devices. The construction of what is currently the most important reactor for fusion research, ITER, is no different. It is being built in the south of France within the framework of an international cooperation. ITER (Latin for “way”) is considered a milestone on the road towards delivering electricity generated by fusion directly to the end user. ITER will be the first fusion experiment to produce 500 million watts of fusion power in pulsed operation for around eight minutes.

Measuring techniques and modelling for ITER

European fusion experiment JET (Joint European Torus). Since 2011, the divertor area of the JET fusion device at the bottom of the picture consist entirely of tungsten elements developed at Jülich. The research centre is strongly involved in the exploitation of this important ITER predecessor.Copyright: EFDA-JET

For this project, Jülich researchers are developing and testing measuring techniques which can be used to accurately record information on factors such as temperatures, densities and magnetic fields as well as on impurities in the plasma. Using the supercomputers at Jülich, they calculate important parameters for the design and construction of future devices. A critical point here is lining the vacuum vessel. For this purpose, Jülich scientists are investigating whether a vacuum vessel wall made of graphite and tungsten would be able to withstand the extremely high loads over the course of years of operation. In the ITER divertor – the most highly loaded area of the walls – scientists expect heat fluxes that are ten times greater that those in aircraft turbines or on the fuel rods of a nuclear power plant.

Instabilities in the plasma can cause even stronger heat pulses for fractions of a second. In addition, the materials must also be resistant to the neutron radiation that occurs due to the nature of the fusion process. In the ITER divertor, solid tungsten is to be used. Jülich scientists and engineers were involved in developing this material, which is currently being tested at JET. JET (Joint European Torus) is located near Oxford in the United Kingdom and is currently the largest and most successful fusion experiment in the world. Forschungszentrum Jülich plays a key role in operating this important ITER forerunner.

Wendelstein 7-X stellarator possible alternative to tokamak

Jülich’s expertise is also much sought after for a fusion device in Germany: the Wendelstein 7-X stellarator in Greifswald, which aims to bring us much closer to implementing a fusion reactor in continuous operation. Forschungszentrum Jülich supports the Max Planck Institute of Plasma Physics in constructing this experiment and is responsible for designing and fabricating important electrotechnical and mechanical components. Jülich thus contributes its extensive technological experience in constructing fusion devices. With its expertise in plasma-wall interaction, Jülich will also play an important role in the scientific use of Wendelstein 7-X. Due to its advantages in continuous operation, the stellarator is considered an attractive alternative to the tokamak concept, which is currently the most advanced type of fusion reactor. Scientific experiment operations at Wendelstein began in February 2016.

Large-scale equipment for fusion research

For their extensive experiments, Jülich scientists together with their partners in Germany and abroad make use of both national and international large-scale facilities in fusion research as well as smaller and more specialized equipment. In Jülich, these facilities are the PSI-2 linear plasma generator, the JUDITH and MARION thermal load experiments as well as numerous laboratory devices; in Germany, the ASDEX Upgrade tokamak and, since 2015, the Wendelstein 7-X stellarator in Greifswald; in the European context, they include the large-scale European experiment JET in the United Kingdom, as well as the Magnum-PSI linear high-flux device in the Netherlands. Experiments on limiting instabilities in the plasma boundary layer are also being conducted by Jülich scientists at the DIII-D tokamak in San Diego, USA.